Finasteride Dosage and Usage for BPH and Androgenetic Alopecia
For benign prostatic hyperplasia (BPH), finasteride should be prescribed at 5 mg once daily, while for androgenetic alopecia, the recommended dosage is 1 mg once daily. 1
Mechanism of Action
- Finasteride is a competitive and specific inhibitor of Type II 5α-reductase that forms a stable enzyme complex, inhibiting the conversion of testosterone to dihydrotestosterone (DHT) 1
- For BPH, finasteride reduces DHT in the prostate by approximately 70%, leading to a 15-25% reduction in prostate size within 6 months 2, 3
- This reduction in DHT causes atrophy most pronounced in the glandular epithelial component of the prostate, which is the source of PSA production 4
Dosage for Benign Prostatic Hyperplasia (BPH)
- The recommended dosage for BPH is 5 mg once daily orally 1
- Treatment should be continued for at least 6 months before evaluating clinical response due to the slow onset of action compared to alpha blockers 2, 5
- Finasteride is most effective in patients with prostatic enlargement (volume >30cc) or PSA >1.5ng/mL 4, 2
- Daily dosing at 5 mg/day reduces serum DHT concentration by approximately 70% 1
Dosage for Androgenetic Alopecia
- The recommended dosage for male pattern hair loss is 1 mg once daily 6
- Even at the lower 1 mg dose, finasteride reduces serum PSA by approximately 40-50% in men aged 40-60 years 6
Clinical Efficacy
- For BPH, patients experience an average 3-4 point improvement in symptom scores (e.g., IPSS), maintained for 6-10 years with continued therapy 4, 2
- Finasteride reduces the risk of acute urinary retention and BPH-related surgery by approximately 55-57% compared to placebo 1
- For androgenetic alopecia, efficacy has been demonstrated primarily in vertex baldness 7
Important Considerations
- PSA levels decrease by approximately 50% after 12 months of therapy; when screening for prostate cancer, the measured PSA value should be doubled to accurately assess disease progression 4, 2
- Finasteride has a slower onset of action compared to alpha blockers; patients should be counseled that symptom improvement may take several months 2, 3
- Using finasteride in patients without prostatic enlargement (<30cc) is ineffective for BPH symptoms 2, 3
Side Effects
- Common side effects include decreased libido (6.4% in first year, 2.6% in years 2-4), erectile dysfunction, and ejaculatory dysfunction (3.7% in first year, 1.5% in years 2-4) 2, 8
- These sexual side effects typically become less common after the first year of therapy 2
- There have been reports of post-finasteride syndrome (PFS), a controversial constellation of sexual, physical, and psychological symptoms that may persist after discontinuation 4, 9
Combination Therapy
- For BPH, combination therapy with an alpha blocker and finasteride provides greater symptom relief than either medication alone, particularly for patients with larger prostates or severe symptoms 2, 3
- Consider combination therapy when immediate symptom relief is desired, as finasteride has a slower onset of action 3
Pharmacokinetics
- Finasteride is well absorbed after oral administration with a bioavailability of 63% 1, 7
- Maximum plasma concentration is reached in 1-2 hours 1
- It is approximately 90% bound to plasma proteins 1, 7
- The elimination half-life averages 6-8 hours 1, 7
By following these dosage recommendations and considering the patient-specific factors outlined above, finasteride can be effectively used to treat both BPH and androgenetic alopecia with appropriate monitoring for side effects and efficacy.